The standoff at the Colorado Springs abortion clinic "has been resolved", with the gunman taken into custody, officials at the scene have confirmed.
Mayor of Colorado Springs John Suthers told journalists the gunman was in custody.
"The situation has been resolved. There's no continuing peril to the citizens of Colorado Springs, but there is a huge crime scene that has to be processed," he said.
At least 11 people, including five police officers, are reported to have been injured.
The gunman at the Colorado Springs Planned Parenthood centre has been captured alive, according to the City of Colorado Springs Twitter account.
The gunman at a US Planned Parenthood clinic is believed to have a high-powered AK47-style weapon, a police source has told NBC News.
The AK47, also known as a Kalashnikov, is a semi-automatic or automatic assault rifle capable of firing off multiple shots in quick succession.
Armed police are on guard in areas surrounding the abortion clinic, as "active shooting" incident continues.
Officials at Planned Parenthood said it is not clear if they were deliberately targeted by a gunman who began shooting at one of their clinics and remains on the loose in Colorado Springs.
"We don't yet know the full circumstances and motives behind this criminal action, and we don't yet know if Planned Parenthood was in fact the target of this attack," said Vicki Cowart, president and CEO of Planned Parenthood of the Rocky Mountains, in a written statement.
She said that the organisation was concerned that "extremists" were fueling "domestic terrorism" within the US, in comments apparently referencing protests and attacks on clinics that provide abortion.
"We will never back away from providing care in a safe, supportive environment that millions of people rely on and trust, " she added.
Colorado Springs Police say people are still being rescued from inside the Planned Parenthood building, amid ongoing shooting.
Two hospitals are treating nine patients from the active shooting scene in Colorado Springs, NBC News reports.
The total number of civilian injuries is unclear.
A patient trapped inside the Planned Parenthood clinic as a gunman began shooting asked her brother to look after her babies in case she did not survive, local media have reported.
Joan Motolinia said that he got a short phone call from his sister Jennifer, aged 28, as she hid underneath a table after shooting started this morning.
"She was very afraid," he told the Denver Post newspaper. "She was telling me to take care of her babies.”
Mr Motolinia said he heard gunshots in the background during the short call. She hung up after around two minutes, and it is not known if she managed to escape the building.
He said that his sister had gone to the appointment alone, and her three children were safe at home.